Some scholars drew a distinction, saying: If the fast was obligatory due to a vow, it should be made up on his behalf; but if it was obligatory by the original prescription of the Sacred Law, it should not be made up on his behalf.

They cited as evidence that a woman came to the Prophet, peace and blessings be upon him, and said, “My mother vowed to fast for a month, but she did not fast.” He said, “Fast on her behalf.” (1) Thus, he permitted her to fast on her behalf. This was a fast due to a vow, and an obligation established by the Sacred Law itself cannot be analogized to it, because the basic principle regarding acts of worship is that appointing another to perform them is not permissible. However, this view is weak.

The correct view is the second opinion: it is permissible to fast on behalf of the deceased for whatever fasting was due from him, whether it was an obligation established by the original prescription of the Sacred Law or an obligation due to a vow. The evidence is the general wording of the hadith of Aishah, may Allah be pleased with her: “Whoever dies owing fasting, his guardian should fast on his behalf.” The case of the woman who asked about the vow is merely one instance covered by this general wording; it neither contradicts nor restricts it. It was a particular incident in which the deceased had died owing an obligatory fast, and the Prophet, peace and blessings be upon him, permitted fasting on her behalf.

Moreover, which is more common: that a person dies owing fasts from Ramadan, or owing a vowed fast? The answer is undoubtedly the former. How often does someone vow to fast and then die before fasting?! It is therefore not possible to apply the general hadith to the rare case while excluding the common one. In reality, this is a flaw in reasoning from the evidence.

Thus, the correct view is that fasting should be performed on his behalf if he dies owing fasting. But when is fasting considered due from him?